A cab and chassis-type truck is commonly fitted with an elongate, hollow, generally cylindrical, closed, horizontally extending, liquid cargo tank. These tanks have historically been fabricated of metal, commonly steel, aluminum or stainless steel, or fiberglass.
Many of the tanks provided for this service have been oval in cross-section, as this gave them a lower center of gravity in comparison to a tank having a circular cross-section.
In recent times, regulatory agencies have been requiring that liquid cargo tanks be formed with a circular cross-section, to obtain the benefit of the higher pressure rating. For example, in the United States, a tank for hauling acid has to have a pressure rating of at least 25 psi. To achieve pressure ratings above normal atmospheric pressure, a tank is usually formed with a circular cross-section. (Tanks of circular cross-section are commonly referred to as "round" tanks.)
Both oval and round liquid cargo tanks made in accordance with the prior art have a bottom discharge assembly for liquid removal (see FIG. 3). More particularly, an opening is formed in the bottom of the wall of the tank. A sump is made integral with the tank wall along the periphery of the opening. The sump has a downwardly facing end wall forming an outlet. A flat flapper valve is mounted to the bottom wall of the sump by inner and outer flanges held together by bolts. Piping is attached to the discharge end of the valve. The piping comprises a downwardly and horizontally projecting elbow and then a horizontal leg of pipe leading to a pump usually mounted on the side of the frame. The piping has to clear the top of the frame.
Using the most common size for outlet piping of 4" diameter, the closest the tank can be positioned to the frame is about 12 inches, to allow the discharge assembly to fit between tank and frame.
When a round tank is mounted in this way on a truck and is loaded, the tank has a relatively high center of gravity and there is a danger the truck may overturn. The danger is less with an oval tank, which has a lower center of gravity.
It is the objective of the present invention to modify oval and round tanks so that each can be cradled closer to the truck frame, to lower the center of gravity of the tank, while still providing the required discharge assembly and not interfering with the frame, drive shaft or the like.